The present invention relates generally to integrated circuit (IC) design, and, more particularly, to power supply management for IC memory devices.
A need for low power electronics has been driven by portable applications, packing density of ICs and conservation of energy. Reducing power supply voltage is an effective way to reduce power consumption of an IC. On the other hand, ever scaling down in semiconductor device sizes demands low supply voltage operations. But small device sizes and low supply voltage cause high leakage and instability in device operations. Cell operation of a static random access memory (SRAM) is one example. FIG. 1 shows a column 100 of SRAM cells 102[0:n], where n is an integer. The SRAM cell 102[0] shown in FIG. 1 has six transistors. Two P-type metal-oxide-semiconductor (PMOS) transistors 110 and 120, and two N-type metal-oxide-semiconductor (NMOS) transistor 115 and 125 form two cross-coupled inverters to store a state in either node C or node D. Two NMOS transistor 130 and 135 serve as pass-gates between a pair of complementary bit-lines (BLs) 140 and 145, and node C and D, respectively. The gates of both the NMOS transistors 130 and 135 are coupled to a word-line (WL) 150. A high voltage power supply (Vcc) line 160 is coupled to the sources of the PMOS transistors 110 and 120 of every cell 102 in the column 100, while a low voltage power supply (Vss) line 170 is coupled to the sources of the NMOS transistors 115 and 125 of the cells 102[0:n]. When writing to the cell 102[0], the complementary BLs 140 and 145 are forced a voltage to overwrite a previous state stored in nodes C or D, therefore, lower Vcc will make the writing easier. When reading from the cell 102[0], the BLs 140 and 145 become driven by nodes C and D, apparently, higher Vcc will make the reading easier. Writing and reading put contradictory demands on the Vcc. As the Vcc scales down with the device sizes, and process variations increase in proportion to the device sizes, it is increasingly difficult for a fixed power supply voltage to meet these contradictory demands.
As such, what is needed is a dynamic power supply that can increase or decrease it voltage on demands.